Method and device for applying a paste

ABSTRACT

In the method described, a compound substantially in the form of a paste is fed by means of a pump from a storage container (1) to a metering device (3) which determines the amount of paste to be applied to a workpiece (B). From the metering device, the paste is fed to a spray head (S) where it is .[.mixed with.]. .Iadd.swirled by .Iaddend.compressed air from a cylinder (4) or other suitable supply and sprayed on to the workpiece (B). The amount of compressed air supplied to the paste for spraying purposes is controlled by means of a control unit (6) in such a way that a strip of substantially constant width is applied to the workpiece (B).

This is .Iadd.a request for reissue of U.S. Pat. No. 5,510,149, whichissued Apr. 23, 1996, which is .Iaddend.a continuation of Ser. No.08/119,207, filed Sep. 22, 1993, (which filing represents thenationalizing of PCT Ser. No. PCT/EP92/00613 filed Mar. 19, 1992) nowU.S. Pat. No. 5,419,930.

FIELD OF THE INVENTION

The invention relates to a method and a device for applying a paste orpaste-like mass, in particular a hardenable glue or sealer, onto aworkpiece, in which the paste is fed by feed pressure to a spray device,in particular to the application nozzle of a spray head, .[.is separatedor mixed by, the action.]. .Iadd.swirled under the influence .Iaddend.ofa compressed gas preferably consisting of compressed air or inert gasand is sprayed onto the workpiece, with the workpiece and the spraydevice being moved relative to one another.

BACKGROUND OF THE INVENTION

In a known method of this type, which is utilized in the industrialprocessing of car-body parts, namely during the gluing of car-body sheetmetal panels, a hardenable glue is sprayed with the help of a spray headonto the edge of the inner surface of an outer car-body sheet metalpanel, which is supposed to be glued to an inner sheet metal panel. Thisis done by the glue being .[.mixed with.]. .Iadd.swirled by.Iaddend.compressed air in the spray head and being then sprayed ontothe edge of the car-body outer sheet metal panel. The width of thesprayed-on strip of glue depends decisively on the relationship betweenthe amount of glue and the amount of compressed air. The inner sheetmetal panel is subsequently placed onto the car-body outer sheet metalpanel and the edge of the outer sheet metal panel, which edge is sprayedwith the glue, is folded around the inner sheet metal panel. Thehardening process can then be activated, for example, by heating thisarrangement.

By spraying on the glue no undesired air pockets occur in the foldduring the hardening operation, which air pockets would bring about adanger of corrosion. However, variations in the consistency of thestrand of glue exiting from the spray head, or in the amount conveyedcan occur during the spray application, which can result in changes inthe width of the strip of glue sprayed onto the workpiece even with aconstant compressed-gas supply. These variations can, for example, bedue to a change in the viscosity of the glue, which in turn can be dueto variations in the temperature or changes in the composition of theglue. This can result either in an incomplete filling of the areas to beglued or in protruding glue. Both cases have disadvantages. When thestrip of glue is too narrow, the gluing of outer sheet metal panel tothe inner sheet metal panel is insufficient, whereas when the strip ofglue is too wide glue can protrude over the edge of the fold, which canlead to difficulties during the hardening operation and during the latercleaning operation.

Starting out from this, an object of the invention is to develop amethod and a device of the above-mentioned type, with which an evenapplication of glue onto the workpiece surface is guaranteed.

To attain this purpose the invention suggests that the amount ofcompressed gas supplied per unit of time and/or its flow speed iscontrolled in such a manner that a strip of paste of an essentiallyconstant width is sprayed on along the workpiece.

In order to achieve this, it is possible according to an advantageousdevelopment of the invention to measure the feed pressure of the pasteprior to its entry into the spray device and to control the amount ofcompressed gas supplied per unit of time in functional dependency of themeasured feed pressure.

A further advantageous or alternative development of this method is tomeasure the temperature of the paste prior to its entry into the spraydevice and to control the amount of compressed air or inert gas infunctional dependency of the measured temperature.

A further advantageous development of the invention provides that thevolume or mass stream of the paste is adjusted to a desired value byvarying the feed pressure at a constant flow cross section of the spraydevice. This is done, for example, in such a way that the .[.feed.]..Iadd.volume .Iaddend.or mass stream is adjusted to a predeterminedvalue by varying the driving pressure or the electrical drivingperformance of a preferably electrically driven metering device. Thecompressed gas supplied per unit of time can in this case be controlledin functional dependency of the driving pressure or rather the drivingperformance or the driving voltage level derived therefrom. The.Iadd.volume .Iaddend.stream .[.volume.]. can thereby be measureddirectly by means of a flow meter or indirectly through the piston speedof a metering cylinder forming the metering device. The functionaldependency between the compressed-gas supply and the measuring parameterdetermining the compressed-gas supply can be provided, for example, inthe form of a stored digital or analog, empirically determinedcalibration curve.

At varying mass flow through the spray device it is basically alsopossible to control the relative speed between spray device andworkpiece in such a manner that the same amount of paste per unit areais sprayed onto the workpiece.

According to the device the object of the invention can be attained byproviding a device for controlling the compressed-gas supply to thespray head, through which the compressed-gas supply is controlled inaccordance with a desired width of the strip of glue applied along theworkpiece.

The device of the invention includes a storage container for the paste,a feed pump for feeding the paste to a metering device, a furtherstorage container or a supply connection for the compressed gas and avalve for controlling the compressed-gas supply to a spray head, withthe spray head .[.mixing.]. .Iadd.swirling .Iaddend.the paste comingfrom the metering device with compressed gas and spraying it onto theworkpiece, while the workpiece and the spray head are being movedrelative to one another. A valve for the compressed-gas supply is inthis case controlled through the control device in such a manner thatthe spray head sprays a strip of paste of an essentially constant widthon along the workpiece.

An advantageous development of the invention provides a pressure sensorfor measuring the feed pressure, which pressure sensor is arranged infront of the spray head, or a temperature sensor for measuring thetemperature of the paste and a device for controlling the compressed-gassupply to the spray head, which device reacts to the measured feedpressure or the measured mass temperature.

A regulator is advantageously arranged in front of the spray head,through which regulator the volume or mass stream of the paste can beadjusted to a predetermined desired value by varying the feed pressureat a constant flow cross section in the spray head. In addition apreferably electrically driven metering pump for the paste, whichmetering pump can be controlled through the regulator, and a device forcontrolling the compressed-gas supply to the spray head, which devicereacts to the driving pressure or rather the driving performance orvoltage level of the metering pump, are provided. The volume or massstream can be measured with the help of a flow meter arranged in frontof the spray head in the feed pipe or with the help of a device formeasuring the piston speed of a metering cylinder forming the meteringpump, while the device for controlling the compressed-gas supplycontains advantageously an analog or digital calibration-curvegenerator.

The measures of the invention give consideration to the knowledge thatdepending on the viscosity or stiffness of the glue a more or lessviscous strand of glue exits from the application nozzle of the sprayhead. On the other hand, depending on the viscosity of this strand amore or less large amount of air or air speed is needed in order toselectively guide the strand in order to thus arrive at a specific stripwidth. The functional interrelations in this regard are givenconsideration according to the invention with the help of theempirically determined and electronically stored calibration curve.

The paste can be supplied through a metering cylinder to the applicationnozzle in the spray head. The piston speed is measured in this case asan indication of the volume of the amount of glue applied per unit oftime. The driving pressure acting onto the piston is available as afurther measurement. The pressure is higher at a pregiven metered amountwhen the viscosity of the paste is high. This pressure is thus anindirect measurement for the viscosity of the paste, which in turndepends on the temperature and on the composition of the paste. Thedriving pressure is usually produced through a feed system acting ontothe piston, which feed system is, for example, electrically driven. Theelectrical voltage, which is applied to the feed system and which isessentially pressure-proportional, can thus be measured as a controlvariable for the feed control and thus as a stream volume controlvariable, and as a control variable for the compressed-gas supply to thespray head taking into consideration the previously-mentionedcalibration curve. From a physical viewpoint this means that the voltagevalue measured at the feed system at a constantly adjusted mass rate offlow is a measurement for the stiffness or viscosity of the strand ofmass exiting from the application nozzle.

In particular in the case of large technical applications, in which thepaste is not supplied through a metering cylinder, but through anannular pipeline, which is tapped at individual stations, measuring thefeed stream is necessary with the help of a flow-measuring device, forexample a gear measuring cell or an inductive measuring cell in order tocarry out control over a stream volume. Furthermore a pressure sensorarranged as much as possible near the application nozzle is additionallyneeded in this case, through which the compressed-gas supply (also inaccordance with an empirical calibration curve) is controlled.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be discussed in greater detail hereinafter inconnection with the drawing. The single FIGURE shows a block diagram ofa preferred exemplary embodiment of a paste-applying device.

DETAILED DESCRIPTION

The paste-applying device illustrated in the block diagram contains astorage container 1 for the paste and a feed pump 2, which feeds thepaste from the storage container 1 to a metering device 3. The outlet ofthe metering device is connected to a spray head S. Sensors 7(illustrated by dashes) are furthermore provided on the path to thespray head S. A further storage container 4 or a connection for acompressed gas (compressed air or inert gas) is connected to a valve V,with which the compressed-gas supply to the spray head S can becontrolled. The block diagram shows furthermore a desired-value adjusteror regulator 5, which is connected to both the metering device 3 andalso to a control device 6. The control device 6 is connected on theinlet side additionally to the outlet of the respective sensor 7, whileit is connected on the outlet side to the control inlet of the valve V,which is for example constructed as a proportional valve.

The paste, which is for example a hardenable glue or sealer, is movedfrom the storage container 1 with the help of the feed pump 2 to themetering device 3. The amount of glue or sealer, which is to be appliedper unit of time onto a workpiece, for example onto a piece of sheetmetal B for use as an automobile body panel, is adjusted by thedesired-value adjuster 5 and is forwarded in the form of an electricalsignal to the metering device 3, which, based on this desired value,conveys the desired amount of glue or sealer to the spray head S. Anexample for the design of such a spray head S is described in EP-A-O 367985.

The strand of glue or sealer exiting from the paste-applying nozzle ofthe spray head S is .[.mixed with.]. .Iadd.swirled by .Iaddend.thecompressed air arriving through the valve V and is sprayed onto thesheet metal B. The spray head S and the workpiece B are at the same timemoved relative to one another in a direction of the strip to be applied.In order to obtain a constant strip width on the workpiece B, the samecompressed-air stream must be continuously supplied at a constantviscosity of the glue or sealer. The desired value for the amount of airto be .[.admixed with.]. .Iadd.supplied to .Iaddend.the glue isforwarded to the control device 6 from the desired-value adjuster 5,through which control device 6 in turn adjusts the cross section of thethroughlet of the valve V.

If during the operation, variations in the temperature and thecomposition, and thus in the viscosity of the glue occur, then the feedpressure must follow accordingly at a pregiven flow of the mass. Becauseof the simultaneously occurring change in viscosity, the compressed-airsupply needs also to be changed in order to arrive at the same stripwidth. This is done with the help of a calibration-curve generatorcontained in the control device 6, the variable parameters of which areempirically determined and adjusted. The magnitudes of the regulating orcontrolling variables, such as the weight rate of flow, pressure, ortemperature, are detected with the help of the sensors 7 at the outletside of the metering device 3 or at the inlet side of the spray head Sand are preferably forwarded in the form of electrical signals to thecontrol device 6 for the purpose of controlling the valve V. With thisit can be achieved that the amount of compressed air, which is.[.mixed.]. .Iadd.swirled .Iaddend.with the stream of glue or sealer, iscontrolled such that the same spray width is obtained at all times. Thusthe problems of an excessive or reduced application of glue or sealerare avoided and a safe gluing of the workpieces is guaranteed.

The sensors 7 are advantageously designed as a temperature sensor,pressure sensor or as an amount-measuring cell. It is also possible tothereby provide several sensors, for example, one at the outlet of themetering device 3 and one at the glue inlet into the spray head S.

Epoxy-resin glues, glues having a polyurethane base or acrylate gluesare, for example, suitable for use as glue and sealer; however, alsoother types of glues are suitable. The paste does not necessarily haveto be a glue or sealer. The described device or rather the methodcarried out with this device is principally suited also for otheressentially paste-like materials, the viscosity of which can vary inwide limits and which, in spite of this characteristic, are supposed tobe evenly applied onto a workpiece B.

The above described device or the method carried out with this deviceare particularly suited for use in industrial manufacturing, inparticular in connection with an industrial robot.

In summary the following is to be stated: An essentially paste-likecompound is fed from a storage container 1 by means of a feed pump 2 toa metering device 3, which determines the amount of paste to be appliedonto a workpiece B. The paste is guided to a spray head S, where it is.[.mixed with.]. .Iadd.swirled by .Iaddend.compressed air from a furtherstorage container 4 or through a suitable connection and is sprayed ontothe workpiece B. The amount of compressed air, which is fed to the pastefor spraying, is thereby controlled by means of a control device 6 insuch a manner that a strip of an essentially constant width is sprayedonto the workpiece B.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method for applying apaste material to a workpiece which is moveable relative to a spraydevice, the method comprising the steps of:feeding the paste material tothe spray device by the action of a feed pressure; .[.separating and/ormixing the paste material with a compressed gas within the spray device;spraying the paste material onto the workpiece with the workpiece andthe spray device being moved relative to one another;.]. .Iadd.sprayingthe paste material in the form of a strand onto the workpiece with theworkpiece and the spray device being moved relative to one another;swirling the strand of paste material with a compressed gas; .Iaddend.measuring a temperature of the paste material prior to its entry intothe spray device; and controlling the amount of compressed gas suppliedper unit of time to the paste material in functional dependency on themeasured temperature, so that a strip of paste material of essentiallyconstant width is sprayed on along the workpiece.
 2. The method of claim1, further comprising the step of setting the functional dependencyusing a stored digital or analog, empirically determined calibrationcurve.
 3. The method of claim 1, further comprising the step ofcontrolling the relative velocity of the spray device and the workpieceso that an amount of paste material sprayed onto the workpiece per unitarea is maintained constant.
 4. A method for applying a paste materialto a workpiece which is moveable relative to a spray device, the methodcomprising the steps of:feeding the paste material to the spray deviceby the action of a feed pressure; .[.separating and/or mixing the pastematerial with a compressed gas within the spray device; spraying thepaste material onto the workpiece with the workpiece and the spraydevice being moved relative to one another;.]. .Iadd.spraying the pastematerial in the form of a strand onto the workpiece with the workpieceand the spray device being moved relative to one another; swirling thestrand of paste material with a compressed gas; .Iaddend. determiningthe feed pressure of the paste material as a measure of its viscosityprior to its entry into the spray device; adjusting a volume or massstream of the paste material to a set value by varying the feed pressureat a constant flow cross section of the spray device; and controllingthe amount of compressed gas supplied per unit of time to the pastematerial in functional dependency on the measured feed pressure so thata strip of paste material of essentially constant width is sprayed onalong the workpiece.
 5. The method of claim 4, wherein the step ofadjusting the volume or mass stream to the set value includes varying adriving pressure or the electrical driving power of an electricallydriven metering device to vary the feed pressure.
 6. The method of claim5, wherein the feed pressure is dependent upon a driving pressure, adriving power or a driving voltage level of the metering device, thestep of controlling the amount of compressed gas supplied per unit oftime being in functional dependency on the driving pressure or drivingpower of the metering device or the driving voltage level derivedtherefrom.
 7. The method of claim 4, further comprising the step ofdirectly measuring the volume or mass stream of the paste material witha flow meter or indirectly measuring the volume or mass stream of thepaste material by measuring a piston speed of a metering cylinderforming a metering device.
 8. The method of claim 4, further comprisingthe step of setting the functional dependency using a stored digital oranalog, empirically determined calibration curve.
 9. The method of claim4, further comprising the step of controlling the relative velocity ofthe spray device and the workpiece so that an amount of paste materialsprayed onto the workpiece per unit area is maintained constant.
 10. Adevice for applying a strip of a paste material to a workpiece,comprising:a spray head moveable relative to the workpiece; means forsupplying said paste material into said spray head.Iadd., said sprayhead forming a strand of the paste material.Iaddend.; means forsupplying a compressed gas to the spray head, said compressed gas being.[.mixed with the paste.]. .Iadd.swirled with the strand of paste.Iaddend.material before being applied to the workpiece; temperaturesensing means positioned upstream of the spray head for measuring thetemperature of the paste .[.materials.]. .Iadd.material.Iaddend.;temperature sensitive regulator means for controlling the supply ofcompressed gas to the spray head, dependent on a set width of the massstrip to be applied along the workpiece.
 11. The device of claim 10,further comprising:a storage container for the paste material; feed pumpmeans for feeding the paste material to a metering device; a secondstorage container or a connection for compressed gas; valve means forcontrolling the compressed gas supply to the spray head; control devicemeans for controlling said valve for the compressed gas supply so thatthe amount of compressed gas .[.mixed.]. .Iadd.swirled .Iaddend.with thepaste material per unit of time is metered such that the spray headsprays a strip of paste material of an essentially constant width alongthe workpiece.
 12. The device of claim 10, wherein the regulator meansof the compressed gas supply comprises an analog or digital calibrationcurve generator.
 13. The device of claim 10, further comprisingregulator means for controlling the relative speed of the spray head andthe workpiece such that an essentially constant amount of paste materialper unit area is sprayed onto the workpiece.
 14. A device for applying astrip of paste material to a workpiece, comprising:a spray head moveablerelative to the workpiece; means for supplying said paste material.Iadd.by the action of a feed pressure .Iaddend.to said sprayhead.Iadd., said spray head forming a strand of the pastematerial.Iaddend.; means for supplying compressed gas to the spray head,said compressed gas being .[.mixed with.]. .Iadd.swirled with the strandof .Iaddend.the paste material before being applied to the workpiece;pressure sensing means positioned upstream of the spray head formeasuring the feed pressure of the paste material as a measure of theviscosity of said paste material; paste material regulator meanspositioned upstream of the spray head for adjusting the volume or massstream of the paste material to a set value by varying the feed pressureat a constant flow cross section in the spray head; and feed pressuresensitive regulator means for controlling the supply of compressed gasto the spray head, determined by a set width of the mass strip of pastematerial to be applied along the workpiece.
 15. The device of claim 14,further comprising:metering pump means for the paste material which iscontrolled by the paste material regulator means, the feed pressure ofthe paste material being dependent upon a driving pressure, a drivingpower or a voltage level of the metering pump means; and a device incommunication with said feed pressure sensitive regulator means forcontrolling the compressed gas supply to the spray head, said devicereacting to the driving pressure or the driving power or voltage levelof the metering pump means.
 16. The device of claim 14, wherein theregulator means of the compressed gas supply comprises an analog ordigital calibration curve generator.
 17. The device of claim 14, furthercomprising regulator means for controlling the relative speed of thespray head and the workpiece such that an essentially constant amount ofpaste material per unit area is sprayed onto the workpiece.
 18. Thedevice of claim 14, further comprising flow meter means positionedupstream of the spray head in a feed pipe for determining the volume ormass stream of the paste material.
 19. The device of claim .[.14.]..Iadd.15.Iaddend., further comprising a device for measuring the pistonspeed of a metering cylinder forming the metering .[.device.]..Iadd.pump .Iaddend.as a measure of the volume stream.